The present invention relates generally to integrated lead head suspensions such as those used in magnetic disk drives. In particular, the invention is a method for reducing the electrical resistance of contacts between different layers of conductors in the integrated lead suspensions.
Integrated lead suspensions, and associated components (e.g., integrated lead flexures) are well known and disclosed, for example, in the Bennin et al. U.S. Pat. Nos. 5,893,193, 5,844,751, and 5,982,584. Briefly, these suspensions and components (hereinafter referred to as suspensions) include a copper or copper alloy conductor layer and a stainless steel layer or other spring metal base layer separated by a layer of polyimide or other insulator. Electrical leads used to conduct signals between the read/write head supported by the suspension and the disk drive electronics are formed in the conductor layer.
It is sometimes desirable to use the stainless steel layer of the suspension as a ground or for other signal transmission purposes. One known approach for providing this functionality is to electrically interconnect one of the leads in the conductor layer to the stainless steel layer. Electrical connections of this type can be made by forming a hole or aperture through the conductor and dielectric layers to expose the stainless steel layer. Flowable conductive material such as conductive epoxy adhesive is then deposited into the hole and allowed to set or harden (e.g., when cured at an elevated temperature in the case of thermosetting conductive epoxy). This conductive material functions as an electrical contact between the stainless steel and conductive material layers.
It has been observed that the electrical resistance of conductor-to-stainless steel contacts of the type described above is in the range of 20 ohms or even higher. Oxidation of the surface of the stainless steel in contact with the conductive material is one explanation offered for these relatively high resistance levels. Irrespective of the cause, these resistance levels can reduce the electrical performance of the suspension. There is, therefore, a need for improved electrical contact structures and/or associated resistance reduction methods for use in integrated lead suspensions. In particular, there is a need for structures and/or associated methods for providing integrated lead conductor-to-stainless steel layer electrical contacts having relatively low resistances. Any such structures and methods should be mechanically stable and efficient to fabricate.
The present invention is a method for efficiently producing low electrical resistance contacts between the stainless steel and conductor layers in integrated lead suspensions. The method includes applying an amount of current for a period of time which is effective to reduce the resistance to a desired level. One embodiment of the invention includes applying a 100 mA current for 16 msec to a contact formed by thermosetting conductive epoxy. Contact resistance values can be reduced to less than 1 ohm by the method.